Samsung S23 FE and S24 Ultra features have been ported to the S21 Ultra by an xda member. It has OneUI 7 apps and sounds.
How to download and flash S24 ROM for S21 Ultra
Download and install a custom recovery for Samsung Galaxy S21 Ultra.
Download the ROM from here and this flashable zip from here. You need to be on that ROM before flashing the flashable zip.
Reboot to recovery: to do so power off your Samsung Galaxy S21 Ultra, connect it to a computer via an USB cable and hold both volume up and power on buttons.
Go to install. Flash the ROM zip you downloaded earlier. And in case, you are coming from another ROM, format your data partition.
Features of Elite UI ROM for the S21 Ultra
S23 FE firmware port
Full Galaxy AI
Based on Last S23FE firmware (One UI 6.1.1)
App locker
S23 FE full spoof
Speed Meter
5 bar signal
China Device Care app included
Battery Health section
One UI 7 apps
Secure screenshots and more
One UI 7 sounds